[Feature request] Allow skipping arguments and return values

[myypo]

It would have been great to have an ability to skip certain arguments or all arguments altogether and also not have to have Debug implementation for not logged values.

The reason being that not all arguments/returns can provide reasonable implementations of Debug. Docs of a similiar feature in tokio tracing: https://docs.rs/tracing/latest/tracing/attr.instrument.html#skipping-fields

Not sure yet how difficult it is to implement but in a perfect world it would have been possible to:

1. Choose to skip certain arguments.
2. Choose to skip all arguments.
3. Require Debug only if the value will be actually logged.

/// Logs errors at the `error` level. No log output for `Ok` variant.
#[logcall(err = "error")]
fn divide2(a: usize, b: usize) -> Result<usize, String> {
    if b == 0 {
        Err("Division by zero".to_string())
    } else {
        Ok(a / b)
    }
}

[andylokandy]

Yes, I agree it's convenient to have an attribute config to skip some of the fields. Currently, you could skip all by denoting #[logcall(input = "")] to prevent it from outputting arguments, and also you could manually write the input format string to fine-grained control which arguments to print and using whether Debug/Display like#[logcall(input = "a = {a:?}")].

[myypo]

Unfortunately it seems to me like currently there is no workaround that allows to compile something like this:

struct NonDebuggable;

#[logcall(input = "")]
fn call() -> NonDebuggable {
    NonDebuggable {}
}

Because the macro requires all of the function parameters as well as the return value to implement Debug.